1. Field of the Invention
The present invention relates to a tube having a grooved inner surface preferable for a heat exchanger tube for use of a condenser as well as an evaporator which are used in a heat exchanger of an air conditioner or the like and its production method, particularly to a tube having a grooved inner surface achieving high condensing performance and evaporating performance even in a region in which a flow rate of a refrigerant is small and its production method.
2. Description of Related Art
There has conventionally been used a tube having a grooved inner surface having a plurality of spiral grooves at an inner surface of a tube as a heat exchanger tube to promote heat exchanging performance in a heat exchanger such as an air conditioner or the like.
According to heat exchange operation of an air conditioner or the like, there is utilized latent heat in evaporating a refrigerant liquid or condensing a refrigerant gas and in order to promote evaporating performance, there is needed a structure in which the refrigerant liquid is spread over a total of inside of a heat exchanger tube to thereby cause evaporation over an entire heat exchanger surface. In the meantime, in order to promote condensing performance, there is preferably used a structure in which the refrigerant liquid condensed on the heat exchanger surface can easily be removed and the liquid is easy to collect to one location such that the heat exchanger surface is not covered again by the removed liquid.
In recent times, in the case of an air conditioner or the like, in order to achieve energy conservation, there has been requested high heat exchanger performance (evaporating as well as condensing) and accordingly, it is indispensable to use a high heat exchanger performance tube even under a condition of small running load, that is, even in a region of a small flow rate of the refrigerant.
There have conventionally been proposed heat exchanger tubes shown below as tubes having grooved inner surfaces in which the inner surfaces of the tubes are fabricated to promote the heat exchanger performance.
According to a heat exchanger tube described in Japanese Unexamined Patent Publication No. 4-158193, there are installed a plurality of kinds of spiral groove groups. These spiral groove groups are formed such that at least one or more of factors in a pitch of groove in respect of a tube axis direction among adjacent spiral grooves, dimensions of the groove, the shape of the groove and a twist angle of the groove group in respect of the tube axis direction, differs.
Further, according to a heat exchanger tube described in Japanese Unexamined Patent Publication No. 8-121984, there are installed a plurality of continuous fins formed not to intersect with each other in the tube axis direction, discontinuous fins formed contiguous to the continuous fins in a discontinuous or sawtooth-like shape along a longitudinal direction such that the discontinuous fins do not intersect with the continuous fins and grooves formed between the discontinuous fins and the continuous fins.
Furthermore, according to a heat exchanger tube with grooves crossing an inner surface which is described in Japanese Unexamined Patent Publication No. 8-178574, in which grooves are formed at an inner surface of the tube to be inclined by 7xc2x0 through 25xc2x0 to the tube axis and sub grooves are installed in parallel with the tube axis or burrs are installed at three-dimensional projections left among the main grooves and the sub grooves to thereby conduct flow of the refrigerant in the direction of the sub groove.
Still further, according to a heat exchanger tube having a grooved inner surface described in Japanese Unexamined Patent Publication No. 10-206060, there are installed a first and a secondgroove group having the same groove pitch in a tube circumferential direction and different twist angles and twist directions in respect of the tube axis direction, there are arranged a plurality of sets of a first and a second groove fabricating region formed with the first and the second groove groups with different widths and there are arranged linear groove regions extending in the tube axis direction among the respective groove fabricating regions.
However, there are problems shown below in the above-described conventional heat exchanger tubes. First, according to the heat exchanger tube described in Japanese Unexamined Patent Publication No. 4-158193, although the flow of the refrigerant liquid is not hindered, the pressure loss cannot sufficiently be reduced in evaporation and accordingly, the evaporating performance is deteriorated and since discharge performance of the condensing refrigerant liquid is not sufficient in condensation, the performance of bringing the heat exchanger surface in contact with the refrigerant gas is lowered to thereby deteriorate the condensing performance. Further, when spiral groove groups having the same twist angle in respect of the tube axis direction are provided over the entire inner surface of the tube, the condensing refrigerant liquid is liable to spread over the entire heat exchanger surface in condensation, the heat exchanger surface is covered by the condensing refrigerant liquid and the condensing performance is deteriorated.
Further, according to the heat exchanger tube described in Japanese Unexamined Patent Publication No. 8-121984 and Japanese Unexamined Patent Publication No. 8-178574, the heat exchanger surface is designed with continuous grooves as a reference and accordingly, when the heat exchanger tube is used for a condenser, a swirl flow of the condensed refrigerant gas is liable to produce along the grooves. As a result, it is difficult to procure a dry heat exchanger surface necessary for condensation and accordingly, a deterioration in the condensing performance is resulted. Accordingly, there is a drawback in which the heat exchanger tube is not preferable in a heat pump type air conditioner requesting the evaporating performance and the condensing performance.
Further, according to the heat exchanger tube described in Japanese Unexamined Patent Publication No. 10-206060, there poses a problem in which the evaporating performance is deteriorated since a swirl flow of the refrigerant is hindered by the grooves in the reverse direction under a condition of a small flow rate of the refrigerant.
As mentioned above, in any of the conventional technologies, there are advantages and disadvantages and the performance excellent both in the evaporating and the condensing cannot be ensured.
The present invention have been carried out in view of such problems and it is an object of the present invention to provide a tube having a grooved inner surface capable of achieving high condensing performance and high evaporating performance even in a region of a small flow rate of a refrigerant and preferable as a heat exchanger tube for a condenser and an evaporator and its fabrication method.
According to an aspect of the present invention, there is provided a tube having a grooved inner surface comprising spiral groove fabricating zones formed with spiral grooves at an inner surface of a metal or an alloy tube, intersecting groove fabricating zones arranged at regions different from regions of the spiral groove fabricating zones at the inner surface of the metal or the alloy tube and formed with intersecting groove groups intersected with pluralities of grooves, wherein singles or pluralities of the spiral groove fabricating zones and the intersecting groove fabricating zones are arranged alternately in an inner peripheral direction of the metal or the alloy tube and when a fabrication width of the spiral groove fabricating zone in the inner peripheral direction is designated by a notation W1 and a fabrication width of the intersecting groove fabricating zone is designated by a notation W2, a ratio W1/W2 of W1 to W2 falls in a range of 0.3 through 0.9 or 1.1 through 3.0.
According to the present invention, in the case in which the tube having the grooved inner surface according to the present invention is used for an evaporator, when a refrigerant liquid is supplied to inside of the tube having the grooved inner surface, since the intersecting groove groups intersected with the plurality of groove groups to each other are formed in the intersecting group fabricating zones, intersecting groove portions intersected with the respective grooves constitute boiling nuclei, evaporation of the refrigerant liquid is expedited and therefore, the evaporating performance can be promoted.
In the meantime, when the tube having the grooved inner surface is used for a condenser, when the refrigerant gas is supplied to inside of the tube having the grooved inner surface, the refrigerant gas is brought into contact with a heat exchanger surface and cooled to condense. The condensed refrigerating liquid is going to produce a swirl flow along the groove groups formed in regions having a wider fabrication width, since the inertia of flow of the condensed liquid of the refrigerant gas at an initial stage of liquefaction is small, the flow of the swirl flow is restrained by the spiral groove groups formed in regions having a narrower width and inclined in the reverse direction. Therefore, the condensed liquid of the refrigerant gas is liable to collect to the lower portion of the tube having the grooved inner surface by the gravitational force, the total of the heat exchanger surface is not covered by the condensed liquid of the refrigerant gas and at the upper portion in the tube having the grooved inner surface, the heat exchanger surface is always brought into contact with the refrigerant gas, continuous condensation is maintained and accordingly, high condensing performance can be achieved.
Further, when W1/W2 is less than 0.3, the flow of the swirl flow of the refrigerant is expedited and the evaporating performance is promoted, however, the condensed liquid produced by condensing the refrigerant gas is liable to spread over the entire heat exchanger surface and covers the heat exchanger surface and therefore, contact between the heat exchanger surface and the refrigerant gas is hindered and therefore, the condensing performance is deteriorated. In the meantime, when the W1/W2 exceeds 0.9 and is equal to or lower than 1.0, although the condensing performance is promoted, the evaporating performance is lowered since the swirl flow of the refrigerant is restrained by the spiral groove groups of the spiral groove fabricating zones.
Further, when W1/W2 is less than 1.1, although the condensing performance is promoted, the effect of restraining the swirl flow of the refrigerant by the intersecting groove portions of the narrow intersecting groove fabricating zones is increased and the evaporating performance is lowered. In the meantime, when W1/W2 exceeds 3.0, although the swirl flow of the refrigerant is expedited and the evaporating performance is promoted, the condensed liquid liquefied in condensation is liable to spread over the entire heat exchanger surface of the tube having the grooved inner surface, the condensed liquid covers the exchanger surface of the tube having the grooved inner surface, contact between the refrigerant gas and the heat exchanger surface is hindered and the condensing performance is deteriorated. Accordingly, by setting W1/W2 to fall in a range of 0.3 through 0.9 or setting W1/W2 to fall in a range of 1.1 through 3.0, high performance can be achieved in both of the evaporating performance and the condensing performance.
Further, it is preferable that a twist direction relative it to a tube axis of the metal or the alloy tube of one groove group in the intersecting groove groups formed in the intersecting groove fabricating zones, is formed in a direction reverse to a direction of the spiral grooves and a groove bottom width of the one groove group is formed wider than a groove bottom width of the other intersecting groove groups. In this case, the one groove group can be formed such that a groove bottom thereof is continuous in the longitudinal direction and a groove bottom of the other groove group is intermittent in the longitudinal direction. In this way, by making continuity of the one groove group stronger than that of the other groove group, the refrigerant liquid produces the swirl flow along the one groove group having the continuity stronger than that of the other groove group and is spread over the entire inner surface of the tube. Accordingly, the evaporating performance of the tube having the inner surface groove can further be promoted.
A fabrication method of a tube having a grooved inner surface according to the present invention is featured in that a surface of a strip-like streak member comprising a metal or an alloy is formed, by rolling, with the intersecting groove fabricating zones and the spiral groove fabricating zones under conditions specified in the above-described aspects of the present invention and butted end portions thereof are welded while rounding the streak member with a surface thereof formed with the intersecting groove fabricating zones and the spiral groove fabricating zones disposed on an inner side.